This ANS-C01 practice question tests your understanding of network implementation. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company is designing a VPC with multiple subnets for a three-tier application. They need to ensure that the database tier (private subnet) can be accessed only by the application tier (private subnet) and that no other resources in the VPC can access the database. Which TWO security mechanisms should be used together to achieve this? (Choose TWO.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Security groups
Option A (Network ACLs) and Option D (Security groups) are correct. Network ACLs provide stateless filtering at the subnet level, and security groups provide stateful filtering at the instance level. By configuring both, you can restrict access to the database subnet only from the application subnet. Option B is incorrect because VPC Flow Logs are for monitoring, not access control. Option C is incorrect because an IAM policy controls permissions for AWS API calls, not network traffic. Option E is incorrect because a route table controls routing, not filtering.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Route tables
Why it's wrong here
Incorrect; route tables determine traffic paths, not allow/deny decisions.
✗
VPC Flow Logs
Why it's wrong here
Incorrect; Flow Logs capture traffic information but do not control access.
✓
Security groups
Why this is correct
Correct; security groups act as virtual firewalls at the instance level.
Incorrect; IAM controls API access, not network traffic.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Security groups — Option A (Network ACLs) and Option D (Security groups) are correct. Network ACLs provide stateless filtering at the subnet level, and security groups provide stateful filtering at the instance level. By configuring both, you can restrict access to the database subnet only from the application subnet. Option B is incorrect because VPC Flow Logs are for monitoring, not access control. Option C is incorrect because an IAM policy controls permissions for AWS API calls, not network traffic. Option E is incorrect because a route table controls routing, not filtering.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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